The background of turbomachinery is well known in the art and familiarity with such art is presumed. The details of a typical prior art turbine are disclosed in U.S. Pat. No. 4,863,343, which is issued to the inventor of the present invention and assigned to the assignee of the present invention. The disclosure of this patent is incorporated herein by reference as if fully set forth.
Typical prior art turbines use a fixed, low restriction flow area at the inner shroud to supply air to the seals and disc cavities. In some designs, however, the pressure required for stator vane cooling is considerably higher than that required for the seals and disc cavities. When this situation occurs the pressure must be raised above the vane and is therefore higher than required for disc cavity flows thereby resulting in excessive leakage. This change is accompanied by reduced engine performance which must be accepted or an additional compensating pressure drop must be built into the system at the inner shroud by decreasing the otherwise relatively large inner shroud flow area. However, the added restriction at the inner shroud should be acceptable for nominal design point operation. A problem arises if the disc cavity flow required to maintain acceptably low disc cavity temperatures is higher than expected. Should this situation arise in an assembled, ready to run engine, the only choice is to increase the pressure at the outer vane shroud until sufficient inner shroud flow and acceptably low disc cavity temperatures are obtained. As a result, the outer shroud pressure is now higher than required for vane cooling and preventing contamination, and hence a potentially large additional performance-penalizing flow will be automatically supplied from the compressor bleed system, in addition to what is actually required for the disc cavities.
Therefore, it would be desirable to provide an apparatus and methods by which the pressure required for airfoil cooling in a turbine can be achieved without jeopardizing the lower pressure requirement for supplying air to the interstage seals and disc cavities. Accordingly, it is an object of the present invention to permit the compensation of the pressure within various sections of a turbine engine. It is a further object of the present invention to optimize the pressure distribution within a turbine so as to achieve maximum efficiency and maximize power.